1. Field of the Invention
This invention relates to a piezoelectric ceramic composition not containing lead in the composition, its production method, and a piezoelectric device and a dielectric device each using the piezoelectric ceramic composition as its material.
2. Description of the Related Art
A PZT (PbTiO3—PbZrO3) component system ceramic containing lead has been used in the past as a piezoelectric ceramic composition.
The PZT described above is excellent in an electro-mechanical coupling coefficient and piezoelectric characteristics such as a piezoelectric constant, and a piezoelectric device utilizing PZT has been widely used in sensors, actuators, filters, and so forth. Since PZT has a relatively high relative dielectric constant, it has also been used as a dielectric device such as in capacitors.
Though having excellent characteristics, the piezoelectric ceramic composition formed of PZT contains lead as one of its constituent elements. Therefore, detrimental lead is likely to elute from industrial wastes of products containing PZT and to induce environmental pollution. Concerns about the environment in recent years have made it difficult to produce those products that may result in the environmental pollution, such as PZT. Therefore, development of piezoelectric ceramic compositions not containing lead has been required, and a piezoelectric ceramic composition expressed by the general formula (K1−xNax)NbO3 (with the proviso that 0<x<1) has drawn an increasing attention (“Journal of the American Ceramics Society”, 1962, Vol. 45, No. 5, p209).
However, because sintering of the piezoelectric ceramic composition expressed by the general formula (K1−xNax) NbO3 (with the proviso that 0<x<1) described above is difficult, hot-press sintering must be conducted and the production cost becomes high. The piezoelectric ceramic composition expressed by this general formula involves the problems that piezoelectric constants such as a piezoelectric d31 constant and a piezoelectric g31 constant and an electro-mechanical coupling coefficient Kp are low, a dielectric loss is great and a relative dielectric constant is small. Therefore, though the piezoelectric ceramic composition expressed by the general formula (K1−xNax) NbO3 (0<x<1) is believed to be a novel promising composition that will replace PZT, it has hardly been put into practical application. For this reason, the lead type piezoelectric ceramic composition such as PZT that may invite the environmental pollution has still been utilized widely at present even after the piezoelectric ceramic composition expressed by the general formula described above has been developed.